In transcranial magnetic stimulation, an insulated wire coil is placed on the subject's scalp and brief electrical currents are passed through the coil, creating magnetic pulses that pass into the brain. These pulses generate very small electrical currents in the cortex-the outer part of the brain-briefly disrupting the function of the brain cells in the stimulated area. The stimulation may cause muscle twitching or tingling in the scalp, face and limbs. During the stimulation, the subject will be asked to either keep the hand relaxed or to slightly tense certain muscles in the hand or arm. The test will last about 1.5 hours.